(D) Abrasive wheel machinery.
(1) General
specifications.
(a)
Machine guarding.
Abrasive wheels
will be used only on machines provided with
safety guards as defined in the following paragraphs of this rule,
except:
(i) Wheels used for internal
work while within the work being ground;
(ii) Mounted wheels, used in portable
operations, two inches and smaller in diameter; and
(iii) Types 16, 17, 18, and 18R and 19 cones,
plugs, and threaded hole pot balls where the work offers protection (see
appendix to this rule.)
(b) Guard design.
The safety guard
will cover the spindle end, nut, and flange
projections. The safety guard
will be mounted so as to maintain proper
alignment with the wheel, and the strength of the fastenings
will
exceed the strength of the guard, except:
(i) Safety guards on all operations where the
work provides protection to the operator, may be so constructed that the
spindle end, nut, and outer flange are exposed; and where the nature of the
work is such as to entirely cover the side of the wheel, the side covers of the
guard may be omitted; and
(ii) The
spindle end, nut and outer flange may be exposed on machines, designed as
portable saws, when used with abrasive wheels.
(c) Flanges.
Grinding machines
will be equipped with flanges in accordance with
paragraph (D)(3) of this rule.
(d) Work rests.
(i) On off-hand grinding machines (see
appendix to this rule) work rests
will be used to support the work. They
will be
of rigid construction and designed to be adjustable to compensate for wheel
wear. Work rests
will be kept adjusted to a maximum opening of
one-eighth inch to prevent the work from being jammed between the wheel and the
rest. The employer
will instruct the employee to securely clamp the
work rest after each adjustment. The employer
will also
instruct the employee not to adjust the work rest with the wheel in
motion.
(ii) The work rest
will be
used to support the work wherever practicable.
(e) Excluded machinery.
Natural sandstone wheels and metal, wooden, cloth, or paper
discs, having a layer of abrasive on the surface are not covered by paragraph
(D) of this rule.
(2) Guarding of abrasive wheel machinery.
(a) Cup wheels.
Cup wheels types 6 and 11 (see appendix to this rule)
will be
protected by:
(i) Safety guards as
specified in paragraph (D)(2)(a)(i) of this rule, applies to paragraphs
(D)(2)(a) to (D)(2)(j) of this rule;
(ii) Band type guards as specified in
paragraph (D)(2)(k) of this rule; and
(iii) Special "revolving cup guards" which
mount behind the wheel and turn with it. They
will be made of
steel or other material with strength enough to withstand the shock of the
bursting wheel and
will enclose the wheel sides upward from the back
for one-third of the wheel thickness. The mounting features
will
conform with all
specifications of paragraph (D) of this rule. It
is necessary to maintain clearance between the wheel side and the guard. This
clearance
cannot exceed one-sixteenth inch.
(b) Guard exposure angles.
The maximum exposure angles specified in paragraphs (D)(2)(a)
to (D)(2)(h) of this rule
cannot be exceeded. Visors or other accessory
equipment
will not be included as a part of the guard when
measuring the guard opening, unless such equipment has strength equal to that
of the guard.
(c) Bench and
floor stands.
(i) The angular exposure of the
grinding wheel periphery and sides for safety guards used on machines known as
bench and floor stands
cannot exceed ninety degrees or one-fourth of the
periphery. This exposure
will begin at a point not more than sixty-five
degrees above the horizontal plane of the wheel spindle (see figures 12-1 and
12-2 to this rule, and paragraph (D)(2)(i) of this rule).
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(ii)
Where the nature of the work requires contact with the wheel below the
horizontal plane of the spindle, the exposure
cannot exceed one hundred
twenty-five degrees (see figures 12-3 and 12-4 to this rule).
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(d) Cylindrical grinders.
The maximum angular exposure of the grinding wheel periphery
and sides for safety guards used on cylindrical grinding machines
will
not exceed one hundred eighty degrees. This exposure
will begin at a
point not more than sixty-five degrees above the horizontal plane of the wheel
spindle (see figures 12-5 and 12-6 to this rule, and paragraph (D)(2)(i) of
this rule).
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(e)
Surface grinders and cutting-off machines.
The maximum angular exposure of the grinding wheel periphery
and sides for safety guards used on cutting-off machines and on surface
grinding machines which employ the wheel periphery
will not exceed
one hundred fifty degrees. This exposure
will begin at a
point not less than fifteen degrees below the horizontal plane of the wheel
spindle (see figures 12-7 and 12-8 to this rule).
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(f)
Swing frame grinders.
The maximum angular exposure of the grinding wheel periphery
and sides for safety guards used on machines known as swing frame grinding
machines
will not exceed one hundred eighty degrees, and the
top half of the wheel
will be enclosed at all times (see figures 12-9
and 12-10 to this rule).
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(g)
Automatic snagging machines.
The maximum angular exposure of the grinding wheel periphery
and sides for safety guards used on grinders known as automatic snagging
machines
cannot exceed one hundred eighty degrees and the top
half of the wheel
will be enclosed at all times (see figures 12-9
and 12-10 to this rule).
(h)
Top grinding.
Where the work is applied to the wheel above the horizontal
centerline, the exposure of the grinding wheel periphery
cannot exceed sixty degrees (see figures 12-11 and
12-12 to this rule).
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(i)
Exposure adjustment.
Safety guards of the type described in paragraphs (D)(2)(c) and
(D)(2)(d) of this rule, where the operator stands in front of the opening,
will be
constructed so that the peripheral protecting member can be adjusted to the
constantly decreasing diameter of the wheel. The maximum angular exposure above
the horizontal plane of the wheel spindle as specified in paragraphs (D)(2)(c)
and (D)(2)(d) of this rule
will never be exceeded, and the distance between
the wheel periphery and the adjustable tongue or the end of the peripheral
member at the top
will never exceed one-fourth inch (see figures
12-13, 12-14, 12-15, 12-16, 12-17 and 12-18 to this rule).
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(j)
Material
specifications and minimum dimensions.
(i) See figures 12-31 and 12-32 and table
12-J to this rule for minimum basic thickness of peripheral and side members
for various types of safety guards and classes of service.
(ii) If operating speed does not exceed eight
thousand surface feet per minute cast iron safety guards, malleable iron guards
or other guards as described in paragraph (D)(2)(j)(iii) of this rule
will be
used.
(iii) Cast steel, or
structural steel safety guards as specified in figures 12-31 and 12-32 and
table 12-J to this rule
will be used where operating speeds of wheels are
faster than eight thousand surface feet per minute up to a maximum of sixteen
thousand surface feet per minute.
(iv) For cutting-off wheels sixteen inches
diameter and smaller and where speed does not exceed sixteen thousand surface
feet per minute, cast iron or malleable iron safety guards as specified in
figures 12-31 and 12-32 to this rule, and in table 12-J to this rule
will be
used.
(v) For cutting-off wheels
larger than sixteen inches diameter and where speed does not exceed fourteen
thousand two hundred surface feet per minute, safety guards as specified in
figures 12-22 and 12-23 to this rule and in table 12-A to this rule
will be
used.
(vi) For thread grinding
wheels not exceeding one inch in thickness cast iron or malleable iron safety
guards as specified in figures 12-31 and 12-32 to this rule and in table 12-J
to this rule
will be used.
(k) Band type guards - specifications.
Band type guards
will conform to the following
specifications:
(i) The bands
will be
of steel plate or other material of equal or greater strength. They
will be
continuous, the ends being either riveted, bolted, or welded together in such a
manner as to leave the inside free from projections.
(ii) The inside diameter of the band
will
not be more than one inch larger than the outside diameter of the wheel, and
will be
mounted as nearly concentric with the wheel as practicable.
(iii) The band
will be of
sufficient width and its position kept so adjusted that at no time will the
wheel protrude beyond the edge of the band a distance greater than that
indicated in figure 12-24 and table 12-B to this rule or the wall thickness
(W), whichever is smaller.
(3) Flanges.
(a) General
specifications.
(i)
All abrasive wheels
will be mounted between flanges which
are not
less than one-third the diameter of the
wheel.
(ii) Exceptions.
(a) Mounted wheels;
(b) Portable wheels with threaded inserts or
projecting studs;
(c) Abrasive
discs (inserted nut, inserted washer and projecting stud type);
(d) Plate mounted wheels;
(e) Cylinders, cup, or segmental wheels that
are mounted in chucks;
(f) Types 27
and 28 wheels;
(g) Certain internal
wheels;
(h) Modified types 6 and 11
wheels (terrazzo);
(i) Cutting-off
wheels, types 1 and 27A (see paragraphs (D)(3)(a)(ii)(i)(i) and
(D)(3)(a)(ii)(i)(ii) of this rule);
(i) Type 1
cutting-off wheels are to be mounted between properly relieved flanges which
have matching bearing surfaces. Such flanges
will be at
least one-fourth the wheel diameter;
(ii) Type 27A cutting-off wheels are designed
to be mounted by means of flat, not relieved, flanges having matching bearing
surfaces and which may be less than one-third but not
less than one-fourth the wheel diameter (see figure 12-19 to this rule for one
such type of mounting);
(iii) There
are three general types of flanges: straight relieved flanges (see figure 12-27
to this rule); straight unrelieved flanges (see figure 12-25 to this rule); and
adaptor flanges (see figures 12-28 and 12-29 to this rule);
(iv) Regardless of flange type used, the
wheel
will always be guarded. Blotters
will be
used in accordance with paragraph (D)(3)(f) of this rule.
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(b) Design and material.
(i) Flanges
will be of such
design as to satisfactorily transmit the driving torque from the spindle to the
grinding wheel.
(ii) Flanges
will be
made of steel, cast iron, or other material of equal or greater strength and
rigidity.
(iii) Flanges
will be
designed with respect to rigidity so that when tightened, the radial width of
bearing surface of contact on wheel is maintained (see table 12-F and figure
12-27 to this rule).
(c)
Finish and balance.
Flanges
will be dimensionally accurate and in good
balance. There
will be no rough surfaces or sharp edges.
(d) Uniformity of diameter.
(i) Both flanges, of any type, between which
a wheel is mounted,
will be of the same diameter and have equal
bearing surface. Exceptions are set forth in the remaining
specifications of this rule.
(ii) Type 27 and type 28 wheels, because of
their shape and usage,
need specially designed adaptors. The back flange
will
extend beyond the central hub or raised portion and contact the wheel to
counteract the side pressure on the wheel in use. The adaptor nut which is less
than the minimum one-third diameter of wheel fits in the depressed side of
wheel to prevent interference in side grinding and serves to drive the wheel by
its clamping force against the depressed portion of the back flange. The
variance in flange diameters, the adaptor nut being less than one-third wheel
diameter, and the use of side pressure in wheel operation limits the use to
reinforced organic bonded wheels. Mounts which are affixed to the wheel by the
manufacturer
cannot be reused. Type 27 and type 28 wheels
will be
used only with a safety guard located between wheel and operator during use
(see figure 12-19a to this rule).
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(iii)
Modified types 6 and 11 wheels (terrazzo) with tapered K dimension.
(e) Recess and undercut.
(i) Straight relieved flanges made according
to table 12-F to this rule and figure 12-27 to this rule
will be
recessed at least one-sixteenth inch on the side next to the wheel for a
distance as specified in table 12-F to this rule.
(ii) Straight flanges of the adaptor or
sleeve type (see table 12-G to this rule and figures 12-28 and 12-29 to this
rule)
will be undercut so that there will be no bearing on
the sides of the wheel within one-eighth inch of the arbor hole.
(f) Blotters.
(i) Blotters (compressible washers)
will
always be used between flanges and abrasive wheel surfaces to ensure uniform
distribution of flange pressure (see paragraph (D)(4)(e) of this
rule).
(ii) Exceptions.
(a) Mounted wheels;
(b) Abrasive discs (inserted washer, and
projecting stud type);
(c) Plate
mounted wheels;
(d) Cylinders,
cups, or segmental wheels that are mounted in chucks;
(e) Types 27 and 28 wheels;
(f) Type 1 and type 27A cutting-off
wheels;
(g) Certain internal
wheels;
(h) Diamond and cubic boron
nitride wheels; and
(i) Modified
types 6 and 11 wheel (terrazzo) - blotters applied flat side of wheel
only.
(g)
Multiple wheel mounting.
The driving flange
will be securely fastened to the spindle and the
bearing surface
will run true. When more than one wheel is
mounted between a single set of flanges, wheels may be cemented together or
separated by specially designed spacers. Spacers
will be equal
in diameter to the mounting flanges and have equal bearing surfaces.
(h) Dimensions.
(i) Tables 12-D and 12-F to this rule and
figures 12-25 and 12-27 to this rule show minimum dimensions for straight
relieved and unrelieved flanges for use with wheels with small holes that fit
directly on the machine spindle. Dimensions of such flanges
will
never be less than indicated and should be greater where practicable.
(ii) Tables 12-E and 12-G to this rule and
figures 12-26, 12-28 and 12-29 to this rule show minimum dimensions for
straight adaptor flanges for use with wheels having holes larger than the
spindle. Dimensions of such adaptor flanges
will never be
less than indicated and should be greater where practicable.
(iii) Table 12-H to this rule and figure
12-30 to this rule show minimum dimensions for straight flanges that are an
integral part of wheel sleeves which are frequently used on precision grinding
machines. Dimensions of such flanges
will never be less than indicated and should be
greater where practicable.
(i) Repairs and maintenance.
All flanges
will be maintained in good condition. When
bearing surfaces become worn, warped, sprung, or damaged they
will be
trued, refaced, or replaced. When refacing or truing, care
will be
exercised to make sure that proper relief and rigidity is maintained as
specified in paragraphs (D)(3)(b) and (D)(3)(e) of this rule, and they
will be
replaced when they do not conform to these
specifications and table 12-D to this rule, figure
12-25 to this rule, table 12-E to this rule, figure 12-26 to this rule, table
12-F to this rule, figure 12-27 to this rule, and table 12-H to this rule,
figure 12-30 to this rule. Failure to observe these
specifications might cause excessive flange pressure
around the hole of the wheel. This is especially true of wheel-sleeve or
adaptor flanges.
(4) Mounting.
(a) Inspection.
Immediately before mounting, all wheels
will be
closely inspected and sounded by the employer or a designated employee (ring
test) to make sure they have not been damaged in transit, storage, or
otherwise. The spindle speed of the machine
will be checked
before mounting of the wheel to be certain that it does not exceed the maximum
operating speed marked on the wheel. Wheels shall be tapped gently with a light
nonmetallic implement, such as the handle of a screwdriver for light wheels, or
a wooden mallet for heavier wheels. If they sound cracked (dead), they
will
not be used. This is known as the "ring test."
(i) Wheels
will be dry and
free from sawdust when applying the ring test, otherwise the sound will be
deadened. It should also be noted that organic bonded wheels do not emit the
same clear metallic ring as do vitrified and silicate wheels.
(ii) "Tap" wheels about forty-five degrees
each side of the vertical centerline and about one or two inches from the
periphery as indicated by the spots in figure 12-20 and figure 12-21 to this
rule. Then rotate the wheel forty-five degrees and repeat the test. A sound and
undamaged wheel will give a clear metallic tone. If cracked, there will be a
dead sound and not a clear ring.
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(b) Arbor size.
Grinding wheels
will fit freely on the spindle and remain free
under all grinding conditions. A controlled clearance between the wheel hole
and the machine spindle (or wheel sleeves or adaptors) is essential to avoid
excessive pressure from mounting and spindle expansion. To accomplish this, the
machine spindle
will be made from a nominal (standard) size to
plus .002 inch. A wheel which
has to be forced on a spindle
will
not be used.
(c) Surface
condition.
All contact surfaces of wheels, blotters and flanges
will be
flat and free of foreign matter.
(d) Bushing.
When a bushing is used in the wheel hole it
will
not exceed the width of the wheel and
will not contact the flanges.
(e) Blotters.
A blotter
will be used between the flange and the abrasive
wheel. The blotter
will cover the entire contact area of the flange.
Blotters need not be used with the following types of wheels:
(i) Mounted wheels;
(ii) Abrasive discs (inserted nut, inserted
washer, and projecting stud type);
(iii) Plate mounted wheels;
(iv) Cylinders, cups, or segmented wheels
that are mounted in chucks;
(v)
Types 27 and 28 wheels;
(vi) Type 1
and type 27A cutting-off wheels;
(vii) Certain internal wheels; and
